Loratadine and Cimetidine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Cimetidine
Loratadine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased loratadine serum concentrations; possible loratadine toxicity
Interaction Deep Dive
Coadministered oral doses of loratadine and cimetidine produce an increase in loratadine serum concentrations. No significant adverse effects, however, were reported as a result of this comedication, although the studies were done in healthy volunteers receiving a 10-day course of loratadine3.
Why it happens (mechanism)
Decreased loratadine metabolism
Literature reports
2 reports — tap to read
a) When long-acting loratadine 10 mg per day was given concomitantly with cimetidine 300 mg four times a day, increases in the area under the concentration-time curve (AUC) for loratadine and its major active metabolite descarboethoxyloratadine were 103% and 6%, respectively 1. Twenty-four normal volunteers received a 10-day course of these medications. No clinically relevant changes were found. Clinical effects were assessed by laboratory and cardiographic testing, vital signs, and adverse events. No incidents of sedation or syncope were reported, and no significant alterations in QTc interval occurred. Cimetidine serum concentrations were unaffected.
b) Concomitant administration of loratadine and cimetidine significantly increased the loratadine plasma concentrations and desloratadine concentrations when compared with administration of loratadine alone. Cimetidine concentrations were unaffected by loratadine coadministration. A randomized, evaluator-blind, multiple dose, three-way crossover drug interaction study in which 24 volunteers received either loratadine 10 mg daily or placebo, with cimetidine 300 mg four times daily for 10 days, was conducted. Coadministration of loratadine and cimetidine when compared to loratadine alone increased mean loratadine Cmax from 4.73 to 8.14 ng/mL and AUC (0-24h) from 24.1 to 40.9 ng/mL hr however, desloratadine concentrations remained similar Cmax (5.55 vs 5.25 ng/mL hr) and AUC (0-24h) (88.2 vs 83 ng/mL hr). Compared with administraion of cimetidine alone, coadministration of loratadine and cimetidine gave similar mean cimetidine Cmax (1.64 vs. 1.76 mcg/mL) and AUC (0-24h) (18.1 vs 19.2 mcg/mL hr). No clinically significant changes in cardiac repolarization parameters were observed. The study demonstrated that although a significant pharmacokinetics drug interaction with cimetidine and loratadine exists, this effect was not accompanied by a change in the QT interval 2.
Common questions
Can I take Loratadine and Cimetidine together?
Increased loratadine serum concentrations; possible loratadine toxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Loratadine and Cimetidine interaction?
It is rated minor. Usually limited clinical impact.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Loratadine or Cimetidine need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (3)
- Product Information: Claritin(R), loratadine. Schering Corporation, Kenilworth, NJ, 2000. DailyMed
- Kosoglou T, Salfi M, Lim J, et al: Evaluation of the pharmacokinetics and electocardiographic pharmacodynamics of loratadine with concomitant administration of ketoconazole or cimetidine. Br J Clin Pharmacol 2000; 50:581-589.
- Product Information: Claritin(R), loratadine. Schering Corporation, Kenilworth, NJ, 2000. DailyMed
Keep reading about Cimetidine
Keep reading about Loratadine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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